From the formation of the female egg to the first three hours after fertilization, Drosophila development is controlled by maternal gene expression. During oogenesis, maternal gene products control of development of the oocyte and establish the body axes. Over the years many maternally-acting genes have been identified and characterized. The focus of this proposal is to study the role of one of these genes, lark, during oogenesis. Lark is an RNA-binding protein that has been shown to be important in organization of the actin cytoskeleton. To determine the mechanism of regulation we have identified 38 potential RNA targets, one of which, Dmoesin, is an actin-binding protein. Preliminary evidence shows that Dmoesin protein localization is regulated by Lark, likely through regulation of splicing in the nurse cell nuclei. The experimental design proposed in this application will address the validity of the other 37 potential RNA targets of Lark as well as determine the mechanism of Lark regulation of Dmoesin protein localization. These studies are important since although a lot has been learned about regulation of gene expression and localization in the developing egg chamber, little is known about the role of RNA splicing. These experiments should provide evidence suggesting RNA splicing plays an important role in the regulation of early development.